In the prior art, there is known a driving gap control device that detects a preceding vehicle traveling before a host vehicle and controls a vehicle speed to maintain a predetermined safe driving gap.
In JP 2009-193228 A, there is discussed a driving gap control device that notifies a driver of a lane change timing when a driving gap between a host vehicle and a preceding vehicle is within a predetermined gap necessary to perform a lane change of the host vehicle, and any other vehicle is not detected behind the host vehicle.